DCTH was delisted from Nasdaq but still trading in OTC market as ticker symbol DCTHD, if you haven't sold your stock then its only loss on book not capital loss yet so you cant claim anything however if you have already sold your stock with loss then you can deduct max $3k capital loss. If you have any more question and concern direct message me I will try to clear it.

You need to manage your portfolio. Diversification lowers the risk.

I have charles Schab account and can see transaction Up/down from my phone ,it shows 99.93% loss red font. What does it means ? Do i need to call and tell them now no more DCTH its DCTHD or what?

You dont have to call, your DCTH has changed into DCTHD and now its trading in OTC market , now either you can sell with loss or hold it hoping some miracle will hapen and price goes up around your buy price